Patterned films formed from silicone compositions are used for many applications in the field of electronics, and are particularly useful in the fabrication of integrated circuit chips, optical devices, and MEMS devices. In particular, the patterned films are used for wafer level packaging applications on top of integrated circuits. The patterned films provide several important functions, including dielectric, mechanical and environmental protection. In addition, the patterned films act as a mechanism for redistribution of the connections from the tight pitch (center to center spacing between bond pads) on the integrated circuit chips to the relatively wide pitch required by printed circuit board manufacturers. Further, the patterned films enable stress release in the integrated circuit chips.
Methods of preparing the patterned films include applying the silicone composition onto the substrate to form a film of the silicone composition. After a soft-bake step, a portion of the film is exposed to radiation, typically by placing a photomask having a desired pattern over the film, to produce a partially exposed film that has an exposed region and a non-exposed region. The partially exposed film is then heated for a sufficient amount of time and at a sufficient temperature to substantially insolubilize the exposed region in a developing solvent, with the non-exposed region remaining soluble in the developing solvent. The non-exposed region of the partially exposed film is then removed with the developing solvent to reveal a film-free region and to form the patterned film. The patterned film includes the exposed region that remains on the substrate.
In conventional methods, the film-free region retains residual silicone after removal of the non-exposed region when conventional developing solvents are used. Conventional developing solvents typically include aliphatic hydrocarbon-based solvents, such as Negative Resist Developer (NRD) commercially available from Air Products and Chemicals, Inc. of Allentown, Pa. Other examples of conventional developing solvents include methyl isobutyl ketone, methyl ethyl ketone, n-butyl ether, polyethylene glycol monomethylether, ethyl acetate, y-butyrolactone, nonane, decalin, dodecane, mesitylene, xylene, and toluene.
The residual silicone left on the film-free region affects the performance of the integrated circuits and must be removed. Plasma etching using a fluorine-based plasma is typically used to remove the residual silicone left on the film-free region. Excessive use of fluorine plasma can have negative effects on the integrated circuits. In particular, the fluorine-based plasma degrades PECVD silicon nitride, which may be present on the substrate, as well as other etch-sensitive structures on the substrate. As such, it would be advantageous to reduce or eliminate the presence of residual silicone on the film-free region in order to reduce or eliminate excessive plasma etching that is required to remove the residual silicone.